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Homework Help: Evaluate the change in redshift over 10 years

  1. Dec 11, 2013 #1
    1. The problem statement, all variables and given/known data

    I am given a model where for an accelerating universe the redshift changes according to the following equations (given in part b). For this model and assuming that H0=70km/s/Mpc, evaluate the change in redshift over 10 years, for a source at z=1 and the change in recession velocity

    2. Relevant equations
    rate of change is [itex]\frac{dz}{dt}[/itex]=H0(1+z)-H(z) where H(z) is the Hubble parameter
    In this case I am considering a κ=0 universe with no cosmological constant, so H(z)=H0(1+z)3/2

    3. The attempt at a solution
    I know that the long way would be to take the integral of the [itex]\frac{dz}{dt}[/itex] formula from z=1 to z' over the entire time period. What I am wondering is, because of how minute the change would probably be is it acceptable to approximate this as:
    Δz≈t1H0(1+z-((1+z)3/2)) where t1=10 years?
    Last edited: Dec 11, 2013
  2. jcsd
  3. Dec 12, 2013 #2
    I am asking because when I calculate this I get a negative number for the change in z. Wouldn't this be a blueshift?
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